Làm nhanh giúp em với ạ

Đáp án:

$\text{a) (x + y)($x^{2}$y - x)}$

$\text{= x.($x^{2}$y - x) + y.($x^{2}$y - x)}$

$\text{= x.$x^{2}$y - x.x + y.$x^{2}$y - y.x}$

$\text{= $x^{3}$y - $x^{2}$ + $x^{2}$$y^{2}$ - xy}$

$\text{b) (x + 2y)($x^{2}$ - 2y + 4z)}$

$\text{= x.($x^{2}$ - 2y + 4z) + 2y.($x^{2}$ - 2y + 4z)}$

$\text{= x.$x^{2}$ - x.2y + x.4z + 2y.$x^{2}$ - 2y.2y + 2y.4z}$

$\text{= $x^{3}$ - 2xy +4zx + 2$x^{2}$y - 4$y^{2}$ + 8yx}$

$\text{c) (2xy + 3)(x - 2y)}$

$\text{= 2xy.(x - 2y) + 3.(x - 2y)}$

$\text{= 2xy.x - 2xy.2y + 3.x - 3.2y}$

$\text{= 2$x^{2}$y - 4x$y^{2}$ + 3x - 6y}$

$\text{d) (xy + 2y)($x^{2}$y - 2xy + 4)}$

$\text{= xy.($x^{2}$y - 2xy + 4) + 2y.($x^{2}$y - 2xy + 4)}$

$\text{= xy.$x^{2}$y - xy.2xy + xy.4 + 2y.$x^{2}$y - 2y.2xy + 2y.4}$

$\text{= $x^{3}$$y^{2}$ - 2$x^{2}$$y^{2}$ + 4xy + 2$x^{2}$$y^{2}$ - 4x$y^{2}$ + 8y}$

$\text{= $x^{3}$$y^{2}$ + 4xy - 4x$y^{2}$ + 8y}$

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